Conductive pastes

ABSTRACT

A conductive paste is provided. The conductive paste includes a conductive powder and a resin composition. The resin composition includes a polyester acrylate oligomer, a hydroxyalkyl acrylate (HAA) and a polyvinylpyrrolidone (PVP) derivative. The conductive powder and the resin composition have a weight ratio of 40-85:15-60. The polyester acrylate oligomer, the hydroxyalkyl acrylate (HAA) and the polyvinylpyrrolidone (PVP) derivative have a weight ratio of 15-70:10-60:3-40.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, TaiwanApplication No. 100145025, filed on Dec. 7, 2011, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The technical field relates to conductive pastes.

2. Description of the Related Art

Current conductive pastes mainly comprise resins as a binder andconductive metals as a filler. The more contact among the conductivemetals which enhances electron access among the conductive particles,the more conductivity. However, due to the major difference of physicalproperties between the conductive metals and resins, there are someproblems need to be solved. Therefore, a new conductive paste is needed.

SUMMARY

One embodiment of the disclosure provides a conductive paste,comprising: a conductive powder; and a resin composition, wherein theresin composition comprises a polyester acrylate oligomer, ahydroxyalkyl acrylate (HAA) and a polyvinylpyrrolidone (PVP) derivative.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

One embodiment of the disclosure provides a conductive paste comprisinga conductive powder and a resin composition. The resin compositioncomprises a polyester acrylate oligomer, a hydroxyalkyl acrylate (HAA)and a polyvinylpyrrolidone (PVP) derivative.

The conductive powder may comprise gold, silver, aluminum, copper,nickel, platinum, carbon black or a combination thereof. The conductivepowder may be in a shape of a sheet, grain or a combination thereof. Theconductive powder and the resin composition have a weight ratio of about40-85:15-60.

The polyester acrylate oligomer may be as represented by the followingformula:

(m=1-5) or

(R₁—R₆, independently, are —CH═CH₂ or —CH₂CH₂N((CH₂)_(n)OH)₂ (n=1-15),and at least one of R₁—R₆ is —CH₂CH₂N((CH₂)_(n)OH)₂). The polyesteracrylate oligomer has a viscosity of about 5,000-20,000 cps.

The hydroxyalkyl acrylate (HAA) may be as represented by the followingformula:

(x=1-4).

The polyvinylpyrrolidone (PVP) derivative may be as represented by thefollowing formula:

(R₁, R₂ and R₃ are —H, —OH or —COOH, and y is 50-5,000).

The polyvinylpyrrolidone (PVP) derivative has a molecular weight ofabout 55,000-1,500,000.

The polyester acrylate oligomer, the hydroxyalkyl acrylate (HAA) and thepolyvinylpyrrolidone (PVP) derivative have a weight ratio of about15-70:10-60:3-40.

The conductive paste may further comprise a photoinitiator, aphotosensitizer, a reactive diluent or a combination thereof.

The photoinitiator may comprise2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide,2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO) or a combinationthereof.

The photosensitizer may comprise 2-isopropylthioxanthone,4,4′-(tetraethyldiamino)benzophenone or a combination thereof.

The reactive diluent may comprise acrylic acid, acrylate, polyetheracrylate or a combination thereof.

The weight ratio of the conductive paste and the photoinitiator is about100:0.1-100:10. The weight ratio of the conductive paste and thephotosensitizer is about 100:0.1-100:10. The weight ratio of theconductive paste and the reactive diluent is about 100:0.1-100:10. Theweight ratio of the photoinitiator, the photosensitizer and the reactivediluent is about 0.1-10:0.1-10:0.1-10.

In some embodiments, the conductive paste can be washed out (dissolved)by alcohols. Furthermore, the formulated conductive paste coated on asubstrate through a screen printing process forms a high resolutionpatterned electrode due to the addition of an appropriate amount of PVPtherein to adjust the printing characteristics thereof. The printedmetal electrode possesses excellent conductivity and adhesion due tohigh compatibility and reactivity of the conductive metal powders andthe photosensitive resins in the paste formulation.

In addition, the present conductive paste can be applied as a conductivematerial of various electronic products, for example, touch panels,displays, junctions of small electronic devices and flexible devices.

EXAMPLE 1 Preparation, Compositions and Physical Properties of theConductive Pastes

First, oligomer 223, hydroxyethyl acrylate (HEA), polyvinylpyrrolidone(Mw: 55,000), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide(photoinitiator 819) and 4,4′-(tetraethyldiamino)benzophenone(photosensitizer EMK) were mixed with various weight ratios and stirredto form a paste. Next, silver sheet was added to the paste (aluminumgrain was optionally added to the paste) and mixed by a three-rollermill to form the conductive paste. The fineness of the conductive pastewas controlled to under 20 μm.

The silver sheet (d50=5 μm) was purchased from Taiwan EPI TechnologyIndustries Inc. The aluminum grain (d50=3 μm) was purchased from CerametInc. “d50” means a mesh size of a sieve wherein 50% of the powder canpass therethrough.

Adhesion Test:

The conductive paste was coated on a polyethylene terephthalate (PET)substrate. The adhesion of the conductive paste was then tested by across hatch test method.

Overflowing Test:

After screen printing, a linewidth of a silver electrode line formed ona printed substrate was measured. Using a screen with 188 μm of mesh asan example, when the linewidth of the silver electrode line was largerthan 206.8 μm (188 μm×110%), it meant that the amount of overflowing ofthe conductive paste was larger than 10%. When the linewidth of thesilver electrode line was larger than 244.4 μm (188 μm×130%), it meantthat the amount of overflowing of the conductive paste was larger than30%.

Compositions (weight ratios) and physical properties of variousconductive pastes prepared by the example are shown in Table 1.

TABLE 1 No. 86A 86C 86G 86H 86I 86O 86R 86W Oligomer 15 16.25 12.5 1013.75 9.6 11 3.33 223 HEA 6 3.75 6.25 5 5 4.8 4 11.1polyvinylpyrrolidone 1.5 2.5 3.75 3 3.75 3.6 3 5.55 (Mw: 55,000)Photoinitiator 1.25 1.25 1.25 1 1.25 1 1 1.11 819 Photosensitizer 1.251.25 1.25 1 1.25 1 1 1.11 EMK Silver sheet 75 75 75 75 75 75 75 75Aluminum grain 0 0 0 5 0 5 5 2.8 Adhesion 3B 4B 4B 4B 4B 5B 5B 5B Sheetresistance 1.2-1.5 1.2-1.6 1.3-1.6 0.8-1.0 1.3-1.8 1.5-1.8 1.0-1.20.9-1.1 (Ω/cm²) Amount of <30% <10% <10% <10% <10% <10% <10% <10%overflowing (188 μm)

Amount of overflowing: a ratio between a linewidth of a silver electrodeline and a mesh size of a screen.

The conductive pastes prepared by the example possessed an improvedadhesion (3B above) with the PET substrate. The sheet resistance thereofwas more than 0.8 Ω/cm². The amount of overflowing thereof was less than30%.

COMPARATIVE EXAMPLE 1 Compositions and Physical Properties of OtherConductive Pastes

Compositions (weight ratios) and physical properties of variousconductive pastes are shown in Table 2.

TABLE 2 No. 78D 86K 86X Oligomer 14 0 12.5 223 HEA 4 12.75 10polyvinylpyrrolidone 0 9.75 0 (Mw: 55,000) Photoinitiator 1 1.25 1.25819 Photosensitizer 1 1.25 1.25 EMK Silver sheet 75 75 75 Aluminum grain5 0 0 Adhesion 0B 5B 0B Sheet resistance 1.5-2.0 1.2-1.4 0.8-0.9 (Ω/cm²)Amount of overflowing Serious Serious Serious (188 μm) overflowingoverflowing overflowing (>30%) (>30%) (>30%)

In accordance with Table 2, the conductive pastes of No. 78D and 86X hadno adhesion with the PET substrate and seriously overflowed duringscreen printing (after the screen printing, the linewidth of the silverelectrode line was 30% larger than the mesh size) due to no addition ofpolyvinylpyrrolidone thereto. Additionally, although the conductivepaste of No. 86K contained polyvinylpyrrolidone, the conductive pastealso seriously overflowed during screen printing due to no addition ofthe oligomer thereto.

EXAMPLE 2 Preparation, Compositions and Physical Properties of theConductive Pastes

First, oligomer 2610, hydroxyethyl acrylate (HEA), polyvinylpyrrolidone(Mw: 55,000 or 1,300,000), phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide (photoinitiator 819) and 4,4′-(tetraethyldiamino)benzophenone(photosensitizer EMK) were mixed with various weight ratios and stirredto form a paste. Next, silver sheet was added to the paste (aluminumgrain was optionally added to the paste) and mixed by a three-rollermill to form the conductive paste. The fineness of the conductive pastewas controlled to under 20 μm.

Compositions (weight ratios) and physical properties of variousconductive pastes prepared by the example are shown in Table 3.

TABLE 3 No. 91M 91A 91C 91E Oligomer 15 11 11 7.5 2610 HEA 6.75 4 5.3410 polyvinylpyrrolidone 0 3 2.66 5 (Mw: 55,000) polyvinylpyrrolidone0.75 0 0 0 (Mw: 1,300,000) Photoinitiator 1.25 1 0.5 1.25 819Photosensitizer 1.25 1 0.5 1.25 EMK Silver sheet 75 75 75 75 Aluminumgrain 0 5 5 0 Adhesion 5B 5B 5B 5B Sheet resistance 5.0 1.6-1.8 0.9-1.10.7-0.9 (Ω/cm²) Amount of <30% <10% <10% <10% overflowing (188 μm)

(R₁—R₆, independently, are —CH═CH₂ or —CH₂CH₂N((CH₂)_(n)OH)₂ (n=1-15),and at least one of R₁—R₆ is —CH₂CH₂N((CH₂)_(n)OH)₂) (viscosity of10,000-15,000 cps)

COMPARATIVE EXAMPLE 2 Compositions and Physical Properties of OtherConductive Pastes

Compositions (weight ratios) and physical properties of variousconductive pastes are shown in Table 4.

TABLE 4 No. 91H Oligomer 16.25 2610 HEA 7.5 polyvinylpyrrolidone 0 (Mw:55,000) Photoinitiator 1.25 819 Photosensitizer 0 EMK Silver sheet 75Aluminum grain 0 Adhesion 5B Sheet resistance (Ω/cm²) 1.1-1.8 Amount ofoverflowing Serious overflowing (188 μm) (>30%)

In accordance with Table 4, the conductive paste of No. 91H seriouslyoverflowed during screen printing due to no addition ofpolyvinylpyrrolidone thereto.

EXAMPLE 3 Preparation, Compositions and Physical Properties of theConductive Pastes

First, oligomer 2610, hydroxyethyl acrylate (HEA), polyvinylpyrrolidone(Mw: 55,000), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide(photoinitiator 819) and 4,4′-(tetraethyldiamino)benzophenone(photosensitizer EMK) were mixed with various weight ratios and stirredto form a paste. Next, silver sheet was added to the paste and mixed bya three-roller mill to form the conductive paste. The fineness of theconductive paste was controlled to under 20 μm.

Compositions (weight ratios) and physical properties of variousconductive pastes prepared by the example are shown in Table 5.

TABLE 5 No. 91J 91L 91K 91P 91F Oligomer 14 11.6 40.5 9 6 2610 HEA 4.44.8 40.5 7 8 polyvinylpyrrolidone 0.6 1.6 12.5 2.4 4 (Mw: 55,000)Photoinitiator 1 1 3.25 0.8 1 819 Photosensitizer 0 1 3.25 0.8 1 EMKSilver sheet 80 80 80 80 80 Aluminum grain 0 0 0 0 0 Adhesion 5B 5B 5B5B 5B Sheet resistance 0.4-0.5 0.5 0.34-0.36 0.13-0.17 0.5-0.6 (Ω/cm²)Amount of <30% <10% <10% <10% <10% overflowing (188 μm)

In accordance with Table 5, the conductive pastes of No. 91J, 91L, 91K,91P and 91F had low sheet resistance, even as low as 0.13 (No. 91P), dueto high content of the silver sheet (80 wt %). Therefore, the conductivepastes prepared by the example possessed high conductivity.

COMPARATIVE EXAMPLE 3 Compositions and Physical Properties of OtherConductive Pastes

Compositions (weight ratios) and physical properties of variousconductive pastes are shown in Table 6.

TABLE 6 No. 91N 91O Oligomer 14 13 2610 HEA 4 5 polyvinylpyrrolidone 0 0(Mw: 55,000) Photoinitiator 1 1 819 Photosensitizer 1 1 EMK Silver sheet80 80 Aluminum grain 0 0 Adhesion 5B 5B Sheet resistance (Ω/cm²) 1.1-1.81.7-2.2 Amount of overflowing Serious overflowing Serious overflowing(188 μm) (>30%) (>30%)

In accordance with Table 6, the conductive pastes of No. 91N and 91Oseriously overflowed during screen printing due to no addition ofpolyvinylpyrrolidone thereto.

COMPARATIVE EXAMPLE 4 Compositions and Physical Properties of OtherConductive Pastes

Compositions (weight ratios) and physical properties of variousconductive pastes are shown in Table 7.

TABLE 7 No. PVB PVB PVB PVA (B-72) (B-76) (B-98) Oligomer 13.75 13.7513.75 13.75 2610 HEA 6.25 6.25 6.25 6.25 PVA 2.5 0 0 0 (Mw: 130,000) PVB0 2.5 0 0 (Mw: 170,000-250,000) PVB 0 0 2.5 0 (MW: 90,000-120,000) PVB 00 0 2.5 (Mw: 40,000-70,000) Photoinitiator 1.25 1.25 1.25 1.25 819Photosensitizer 1.25 1.25 1.25 1.25 EMK Silver sheet 75 75 75 75Adhesion NA NA NA NA Sheet resistance NA NA NA NA (Ω/cm²) MiscibilityPoor Poor Poor Poor PVA: polyvinyl alcohol PVB: polyvinyl butyral

In accordance with Table 7, PVA and PVB (soluble in ethanol) wererespectively used to replace polyvinylpyrrolidone. The results indicatedthat the miscibility of the conductive pastes of No. PVA, PVB (B-72),PVB (B-76) and PVB (B-98) (purchased from across company) was poor dueto immiscibility between the conductive pastes, the oligomer and HEA.Therefore, “adhesion” and “sheet resistance” of the conductive pastescould not be further measured.

EXAMPLE 4 Thixotropy of the Conductive Paste

The viscosity of the conductive paste of No. 91P was 817.9 Pa·s at a lowshear rate. However, at a high shear rate, the viscosity thereof wasreduced to 21.02 Pa·s. The results indicated that the alteration of theviscosity of the conductive paste was large when stored and used (bystirring or coating, and other external forces), respectively. That is,the conductive paste possessed an improved thixotropy.

The exemplary photo-curable conductive paste can be washed out(dissolved) by alcohols. Furthermore, the formulated conductive pastecoated on a substrate through screen printing formed a high resolutionpatterned electrode due to adding of an appropriate amount ofpolyvinylpyrrolidone therein to adjust the printing characteristicsthereof. The printed metal electrode possessed excellent conductivityand adhesion due to high compatibility and reactivity of the conductivemetal powders and the photosensitive resins in the paste formulation.

In addition, the exemplary conductive paste can be applied as aconductive material of various electronic products, for example, touchpanels, displays, junctions of small electronic devices and flexibledevices.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A conductive paste, comprising: a conductivepowder; and a resin composition comprising a polyester acrylateoligomer, a hydroxyalkyl acrylate (HAA) and a polyvinylpyrrolidone (PVP)derivative.
 2. The conductive paste as claimed in claim 1, wherein theconductive powder comprises gold, silver, aluminum, copper, nickel,platinum, carbon black or a combination thereof.
 3. The conductive pasteas claimed in claim 1, wherein the conductive powder is in a shape of asheet, grain or a combination thereof.
 4. The conductive paste asclaimed in claim 1, wherein the conductive powder and the resincomposition have a weight ratio of 40-85:15-60.
 5. The conductive pasteas claimed in claim 1, wherein the polyester acrylate oligomer has thefollowing formula:

(m=1-5) or

(R₁—R₆, independently, are —CH═CH₂ or —CH₂CH₂N((CH₂)_(n)OH)₂ (n=1-15),wherein at least one of R₁—R₆ is —CH₂CH₂N((CH₂)_(n)OH)₂).
 6. Theconductive paste as claimed in claim 1, wherein the hydroxyalkylacrylate (HAA) has the following formula:

(x=1-4).
 7. The conductive paste as claimed in claim 1, wherein thepolyvinylpyrrolidone (PVP) derivative has the following formula:

(R₁, R₂ and R₃ are —H, —OH or —COOH, and y is 50-5,000).
 8. Theconductive paste as claimed in claim 1, wherein the polyvinylpyrrolidone(PVP) derivative has a molecular weight of 55,000-1,500,000.
 9. Theconductive paste as claimed in claim 1, wherein the polyester acrylateoligomer, the hydroxyalkyl acrylate (HAA) and the polyvinylpyrrolidone(PVP) derivative have a weight ratio of 15-70:10-60:3-40.
 10. Theconductive paste as claimed in claim 1, further comprising aphotoinitiator, a photosensitizer, a reactive diluent or a combinationthereof.